The specific aims of this study are to perform a Phase I controlled trial using a-difluoromethylornithine (DFMO) to assess toxicity and impact of DFMO on the biological markers, ornithine decarboxylase (ODC) and skin polyamines, in subjects who are organ transplant recipients (OTR). The hypothesis is that DFMO administered to OTR subjects who are at risk of developing skin cancer will inhibit TPA-induced ODC and polyamine levels in the skin, two intermediary markers of carcinogenesis and promotion.